Molten salt reactors (MSRs) represent a fascinating intersection of nuclear history and modern innovation. The concept of using molten salts as both a coolant and fuel carrier dates back to the 1950s, with the pioneering work of Alvin Weinberg and his team at Oak Ridge National Laboratory (ORNL). In 1965, ORNL successfully operated the Molten Salt Reactor Experiment (MSRE), a proof-of-concept reactor that demonstrated the technology’s feasibility and inherent safety features.
The MSRE achieved remarkable results, operating for four years from January 1965 through December 1969, and logging more than 13,000 hours at full power during that time. The trial showcased the MSR’s ability to operate at high temperatures with excellent thermal efficiency, its inherent safety characteristics due to the low-pressure liquid fuel, and its potential for online refueling and fission product removal. Additionally, the MSRE demonstrated the ability to breed fissile material from thorium, a more abundant and readily available resource than uranium.
Despite its success, the molten salt program ended in 1973, with the Atomic Energy Commission deciding to focus on other nuclear reactor designs. However, the knowledge gained from the MSRE project laid the groundwork for future MSR development.
Today, MSRs are experiencing a resurgence of interest worldwide, with numerous companies and research institutions actively developing various designs. MSRs offer several potential advantages, including enhanced safety, reduced waste generation, and the ability to utilize thorium as a fuel source, as previously mentioned.
“There are several molten salt reactor companies that are in the process of cutting deals and getting MOIs [memorandums of intent] with foreign countries,” Mike Conley, author of the book Earth Is a Nuclear Planet: The Environmental Case for Nuclear Power, said as a guest on The POWER Podcast. Conley is a nuclear energy advocate and strong believer in MSR technology. He called MSRs “a far superior reactor technology” compared to light-water reactors (LWRs).
The thorium fuel cycle is a key component in at least some MSR designs. The thorium fuel cycle is the path that thorium transmutes through from fertile source fuel to uranium fuel ready for fission. Thorium-232 (Th-232) absorbs a neutron, transmuting it into Th-233. Th-233 beta decays to protactinium-233 (Pa-233), and finally undergoes a second beta minus decay to become uranium-233 (U-233). This is the one way of turning natural and abundant Th-232 into something fissionable. Since U-233 is not naturally found but makes an ideal nuclear reactor fuel, it is a much sought-after fuel cycle.
“The best way to do this is in a molten salt reactor, which is an incredible advance in reactor design. And the big thing is, whether you’re fueling a molten salt reactor with uranium or thorium or plutonium or whatever, it’s a far superior reactor technology. It absolutely cannot melt down under any circumstances whatsoever period,” said Conley.
Conley suggested that most of the concern people have about nuclear power revolves around the spread of radioactive material. Specifically, no matter how unlikely it is, if an accident occurred and contamination went airborne, the fact that it could spread beyond the plant boundary is worrisome to many people who oppose nuclear power. “The nice thing about a molten salt reactor is: if a molten salt reactor just goes belly up and breaks or gets destroyed or gets sabotaged, you’ll have a messed-up reactor room with a pancake of rock salt on the floor, but not a cloud of radioactive steam that’s going to go 100 miles downwind,” Conley explained.
And the price for an MSR could be much more attractive than the cost of currently available GW-scale LWR units. “The ThorCon company is predicting that they will be able to build for $1 a watt,” said Conley. “That’s one-fourteenth of what Vogtle was,” he added, referring to Southern Company’s nuclear expansion project in Georgia, which includes two Westinghouse AP1000 units. Of course, projections do not always align with reality, so MSR pilot projects will be keenly watched to validate claims.
There is progress being made on MSR projects. For example, in February 2022, TerraPower and Southern Company announced an agreement to design, construct, and operate the Molten Chloride Reactor Experiment (MCRE)—the world’s first critical fast-spectrum salt reactor—at Idaho National Laboratory (INL). Since then, Southern Company reported successfully commencing pumped-salt operations in the Integrated Effects Test (IET), signifying a major achievement for the project. The IET is a non-nuclear, externally heated, 1-MW multiloop system, located at TerraPower’s laboratory in Everett, Washington. “The IET will inform the design, licensing, and operation of an approximately 180-MW MCFR [Molten Chloride Fast Reactor] demonstration planned for the early 2030s timeframe,” Southern Company said.
What may hold MSRs back in the U.S., however, is a lack of understanding within U.S. Nuclear Regulatory Commission circles. “Unfortunately, the Nuclear Regulatory Commission knows everything about light-water reactors—high-pressure, water-cooled, solid-fuel reactors—and knows almost nothing about unpressurized liquid-fuel reactors. So, until they get up to speed, our nuclear technology has to stay within nuclear regulations, and they haven’t studied it enough. So, basically, we’re stuck with using pressurized light-water reactors,” Conley said.
Still, Conley believes there is a path for MSRs to get built sooner rather than later, as he sees regulators in other parts of the world being more open to the technology. “Rest assured, molten salt reactors will be built in the next 10 years, but they will be built overseas,” said Conley.
Source: Power Magazine
